Acoustic target source

ABSTRACT

A plurality of separate channels, each generating a different acoustic frequency band, have connected, in tandem, a random noise generator, a shaping filter, an amplitude clipper, an amplifier and an electro-acoustic transducer. The resulting overall projected acoustic energy level can be selectively shaped with respect to frequency to simulate various target sources.

United States Patent 1 3,706,963

Norstrom et al. 51 Dec. 19, 1972 [$4] ACOUSTIC TARGET SOURCE [56] References Cited [72] Inventors: Wallace C. Norstrom, Waterford; UNITED STATES PATENTS g Welles Mysm' 3,165,734 1/1965 Grodzinsky etal ..340/: D 3,311,868 3/1967 Cupp et al. ..340/s R [73] Assignee: The United States of America as represented by the Secretary of the Navy [22] Filed: on. 7, 1970 21] Appl.No.:78,715"

Primary Examiner--Richard A. Farley Attorney-Richard S. Sciascia, Louis B. Applebaum and Ernest F. Weinberger [S 7 ABSTRACT A plurality of separate channels, each generating a different acoustic frequency band, have connected, in

[52] US. Cl. ..340/5 D, 35/10.4 tandem, a random noise generator, a shaping filter, an [51] 1111. C1. ..H04b 11/00 1 amplitude pp an amplifier and an electro- 5 w f Search 340/3 A, 5 D 5 R, 384 acoustic transducer. The resulting overall projected 35/10 4 acoustic energy level can be selectively shaped with respect to frequency to simulate various target ACOUSTIC TARGET SOURCE The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to projected acoustic energy, and more particularly pertains to the generation of a broad spectrum of acoustic energy whose overall amplitude can be selectively adjusted to simulate a variety of sources.

2. Description of the Prior Art In the field of broadband acoustic noise targets, it has been the general practice to employ the target or generating vehicle to provide the noise. For example, a particular ship might be employed to itself generate the specific target. The use of the target itself has proven unsatisfactory in that not only is it dependent on the availability of the ship, but the amplitude control and bandwidth of the signal are limited.

SUMMARY OF THE INVENTION The general purpose of this invention is to provide an acoustic target source that has all the advantages of similarly employed prior art devices but has none of the above described disadvantages. To attain this, the present invention provides a plurality of separate channels each operative over a specific acoustic frequency spectrum. Each channel includes a random noise source, a selectable shaping filter, a clipper, an amplifier and a transducer. With the components matched, the amplitude output of overall response can be selected to provide simulation of various targets.

An object of the present invention is to provide a simple, reliable, inexpensive and dependable acoustic target source.

Another object is to provide an apparatus for generating an acoustic noise signal in water having selectable or predetermined amplitude and bandwidth.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment made in accordance with the principle of this invention; and

FIG. 2 is a graph of the output of two representative channels of the embodiment of FIG. ll.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the embodiment of the invention illustrated in FIG. l, a plurality of channels (1040), which are functionally identical, all terminating with an electroacoustic element, cover a spectrum from 100 H to ISKI-I The noise generator 111 provides a constant amplitude white noise over the frequency band covered by that channel. (Noise generators of this type are commercially available and may be obtained for any selected spectrum.) The output of the noise generator is applied t the input of a shaping filter 12 which may be esigne to provide the desire shaping, or a vanable shaping filter which can be obtained commercially. In order to ascertain the filter shape, it is necessary to first determine the frequency response of the transducer element 15, which is accomplished by standard techniques. The filter shaping is adjusted to be the approximate inverse of the transducer response over the channel frequency spectrum. Thus, the combined effect of the shaping filter and the transducer is to theoretically provide a constant noise amplitude or some desired slope function. Clipper 13 serves to limit the noise peaks in order to prevent damage to the transducer and to minimize overdriving the amplifier 14 due to the infinite amplitude peaks present in gaussian noise. The amplifier I4 is a power amplifier with adequate volt-ampere capability to produce the required signals across the transducer impedance. The transducer 15 converts the electrical signal applied thereto into acoustic pressure and may be either magnetostrictive or electrostrictive.

The operation of the other channels is identical in function, as described above, except that such channels are designed to produce acoustic signals covering additional frequency bands. The number of channels is determined by the requirement of the intended use, and is not necessarily limited to the frequency coverage indicated. The acoustic energy output vs. frequency was determined from channel embodiments constructed in accordance with FIG. 1 and plotted as shown in FIG. 2. Here the target source was compared to the level of sea-state 6. For simplicity, only two channels are shown, but a similar plot can be derived for all the other channel bands. The same procedure permits simulation of other target sources.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

We claim:

I. An acoustic simulator target source which comprises a plurality of channels each covering a portion of the spectrum and having connected in tandem therein a source of random noise,

variable shaping filters for adjusting the amplitude with respect to frequency for each channel,

an amplitude clipper means for limiting the noise spikes,

an amplifier, and

an electroacoustic transducer,

wherein the amplitude/frequency response of each of said filters is the inverse of the transmitting response of the electroacoustic transducer,

whereby each of said channels will provide an acoustic output which may be adjusted by said filters to simulate the desired target source.

2. The target source according to claim I. wherein said transducer is magnetostrictive and said amplifier is a power amplifier.

l060ll 0756 

1. An acoustic simulator target source which comprises a plurality of channels each covering a portion of the spectrum and having connected in tandem therein a source of random noise, variable shaping filters for adjusting the amplitude with respect to frequency for each channel, an amplitude clipper means for limiting the noise spikes, an amplifier, and an electroacoustic transducer, wherein the amplitude/frequency response of each of said filters is the inverse of the transmitting response of the electroacoustic transducer, whereby each of said channels will provide an acoustic output which may be adjusted by said filters to simulate the desired target source.
 2. The target source according to claim 1 wherein said transducer is magnetostrictive and said amplifier is a power amplifier. 